1. Field of the Invention
The present invention relates to X-ray diagnostic imaging and, in particular, to X-ray diagnostic imaging in a radiation therapy treatment system.
2. Description of the Related Art
The use of linear accelerators in medicine is well known. Such linear accelerators are used for treating patients with radiation therapy, such as X-rays or electron beams. Such X-rays are created when high energy electrons are decelerated in a target material such as tungsten.
In such radiation therapy systems, it is desirable to obtain X-ray images for treatment diagnosis and treatment planning. Typically, radiation therapy systems use full energy electron beams to produce X-rays for diagnostic imaging. These high energy X-rays (about 2 MeV) produce washed out images that are difficult to interpret.
An alternative is to use low voltage sources, but typical low voltage sources are not collinear with the treatment beam. Consequently, the accuracy of the subsequent therapy relies on interpreting the relative position of the two beams.
As such, there is a need for a radiation therapy device that employs low power X-rays for imaging that are substantially aligned with treatment X-rays.
These and other drawbacks in the prior art are overcome in large part by a system and method according to the present invention. A diagnostic target is provided substantially adjacent a treatment target at an X-ray exit window or aperture in a linear accelerator. In a normal or treatment mode, a guide or bending magnet directs an electron beam toward the treatment target, generating X-rays directed at the patient. In a diagnostic mode, the guide magnet is turned off and the electron beam is directed at the diagnostic target such that diagnostic X-rays are directed at the patient. High energy X-rays are absorbed by head shielding. Low energy (about 500 keV) X-rays are used for diagnostic imaging. The high energy treatment beam and the low energy imaging beam are substantially collinear, thereby allowing use of the same beam shielding device hardware in both modes.
A radiation therapy system according to the present invention includes a treatment system and an imaging system. The treatment system employs a first tungsten target to generate high power X-rays for treatment. The imaging system uses a second target to generate low power X-rays for imaging. The targets are arranged such that the resulting treatment and imaging beams are collinear.